Constant speed apparatus



J. l... RUSSELL 1 2,552,296

CONSTANT SPEED APPARATUS Filed Oct. 27, 1944 a a i :z:\ a: A Ci g5} 2222 s? 39 1% v 29 35 e 6 52 50 35 t?! 38 11s.?

. INVENTOR.

Fl 6. 6 $61M Patented May 8, 1951 UNITED STATES PATENT OFFICE CONSTANTSPEED APPARATUS Application October 27, 1944, Serial No. 560,692

3 Claims.

This invention relates to constant speed apparatus, and moreparticularly to a direct current motor of small size and including meanswhereby its running speed may be maintained constant under a widevariety of operating conditions.

In certain mechanisms it is essential that moving parts be driven with avelocity which shall be maintained constant with a high degree ofprecision while the mechanism and the driving motor are subjected tounavoidable wide variations in external conditions. As an example ofdevices wherein this requirement exists may be mentioned meteorologicalinstruments which must be sent aloft in free or captive balloons for thepurpose of determining conditions in the upper atmosphere. In some formsof these instruments a record chart is driven by a small motor andreceives a graphic record of one or more conditions to which theapparatus is exposed. In another form coded signals are sent out byradio waves, to be received at a ground station and there translatedinto a suitable record of conditions characterizing the spacesurrounding the transmitting instrument. In both these forms ofinstruments, and more especially in the latter, it is essential thatcertain elements of the apparaus be driven at a constant velocity, andthat this constancy be maintained without regard to changes intemperature, barometric pressure, position, acceleration, or changes inthe intensity of stored energy from which the apparatus is driven. Thelatter instrument is known by the name of radiosonde, and is Widely usedin meteorological investigations. It has been found that clockwork ofthe conventional type, having a spring motor with an escapement or othermeans for regulating its velocity, in order to be sufliciently powerfulfor the purpose in hand, will have a weight too great for the availablelifting power of the balloon by which the instrument is to be carriedaloft. Furthermore, the design of a clockwork which will operatedependably and with required accuracy through the wide range ofvariables to which such apparatus must be exposed, presents suchelements of design as to render its use generally impracticable.

It is an object of the present invention to provide a miniature motoradapted for operation from a small battery of relatively light weight,and to be sufficiently powerful and efficient that it may dependablyoperate the mechanism of a radiosonde or similar instrument over anextended period of time.

It is a further object of the invention to provide a motor of the aboveclass in which the speed shall be maintained constant at a predeterminedvelocity without respect to such wide changes in battery voltage as mayresult from extremes of temperature or from material weakening of thebattery or long-continued loads.

It is a further object of the invention to provide a motor of the aboveclass which shall maintain its predetermined velocity through widechanges in the temperature to which the motor is exposed.

It is a further object of the invention to provide a motor of the aboveclass which shall maintain its predetermined velocity without respect toposition, orientation, acceleration and barometric pressure.

It is a further object of the invention to provide a motor of the aboveclass which shall be essentially self-starting upon the application of asuitableoperating voltage.

It is a further object of the invention to provide a motor of the aboveclass in which the operating velocity is readily adjustable through awide range of predetermined speed values.

In carryin out the purposes of the invention, the embodiment hereindisclosed provides a motor having a permanently magnetized fieldstructure with which coacts an armature structure having an even numberof salient poles, carrying separate windings having one end of eachconnected to a correspondin segment of a suitable commutator and theother ends brought to a common point including contacts adapted to beopened and closed by means of a centrifugal structure integral with therotatin element.

Other features of the invention will be hereinafter described andclaimed.

In the drawings:

Fig. 1 is a side elevation of a motor embodying the principles of theinvention.

Fig. 2 is an end elevation of the same, having an end-plate removed topermit a clearer View of certain of the operating elements.

Fig. 3 is a view of the same from the opposite end to Fig. 2, having aportion of an end-plate broken away.

Fig. 4 is a bottom elevation of a portion of the apparatus shown in Fig.1.

Fig. 5 is a sectional view of a part of the motor, taken on the line A-Ain Fig. 4.

Fig. 6 is an enlarged view, partly in section, of a centrifugal deviceforming a part of the mechanism of the motor.

Fig. 7 is a diagrammatical view of the electric connections of a motorembodying the principles of the invention.

Fig. 8 is a View of a detail.

Referring now to the drawings:

The field structure of the motor comprises a pair of pole pieces It andII, four identical permanent magnet elements l2, and a combined yoke andjournal member 53. The latter member is formed of ferromagnetic materialsuch as mild steel, and has a substantially cruciform conformation,being provided at the extremity of each of its four arms with anopeni-ng adapted to receive one of four mounting bolts is formed ofnon-magnetic material. Centrally located on the member 13 is a bearing i5, preferably of anti-'- friction metal, and bored to receive the shaftof a rotatable armature presently to be described.

The pole pieces llil i are built up of a suitable number of laminationsof ferromagnetic material, each punched or otherwise formed withperforatiens spaced to facilitate stacking upon adjacent mounting boltsit when the same are positioned in the openings of the member i3, andhaving three sides in substantially rectangular conformation a fourthside concave and of circular curvature Said fourth side of thelaminations are so for-med that when said pole pieces are assembled withtheir concave surfaces facing each other there will be provided a fieldspace adapted to enclose a substantially cylindrical :4,

The four magnet elements M are formed preferably of high-coercive forcematerial, such as Alnico, and are of substantially cylindricalconformation, each having a deep lateral axial groove, to accommodateone of the mounting bolts [4. Each element is permanently magnetized inan axial sense, and When assembled said elements are disposed with thenorth poles of two in magnetic contact with one, and the south poles oftwo in contact with the other, of said pole pieces, and each embracingone of said mounting bolts, whereby when the nuts on said bolts aretightened there will be formed a per-'- manently magnetized fieldstructure having one of the laminated pole pieces of north, and theother of south, polarity and a return path for flux provided by themember H3.

The rotating element of the motor comprises an armature having an evennumber of poles, a commutator, and a centrifugal device carryingelectrical contacts subject to actuation in response to predeterminedvelocity conditions. As shown in the drawings, the magnetic system ofthe armature comprises a laminated structure 2!; having four salientpoles, and mounted on a shaft or spindle 25, of which one end is adaptedt6 be journalle'd for rotation in the bearing it. The pole faces of thestructure 28 are conformed to a common cylindrical curvature coaxialwith the spindle 2 i, and are of such diameter as to provide a minimumrunning clearance from the mid dle portions of the concave surfaces ofthe field pole pieces i@l i. The pole tips of the structure 29 arecircumferentially extended till each subtends a geometrical angle of theorder of '75 degrees, leaving between it and the adjacent p'ole 4 tip aspace of approximately 15 angular degrees. The field and armaturestructures of the motor, as thus far described, comprise a magneticcircuit adapted to utilize with a high degree of efiiciency themagnetomotive force developed by the permanent magnets 82. Anoutstanding advantage lies in the shaping of the field pole faces to acylindrical curvature of greater radius than that of the cylindricalcurvature to which the armature pole faces are conformed. As will beapparent from the drawings, especially Fig. 3, this conformation, inconjunction with the cylindrically disposed armature poles results in anair gap narrow at thecenter and progressively widening toward the fieldpole tips, not only providing flux density gradient conducive todesirable operating conditions in the motor but also tending to minimizediversion of flux through the has of the field and armature poles.

On the respective salient poles of the armature structure are woundsuitable coils 22 of insulated wire, and the terminals of these coilsare connected to a commutator 23 having a number of segmentscorresponding to the number of said poles, and to a centrifugalcircuit-controlling device or governor now to be described.

Fixed t6 the armature shaft .2! is a T-shaped block 25 of solidinsulating material, which may expediently be lucite or an equivalentacrylic resin, adding to desirable electrical and mechan icalcharacteristics the property of transparency, whereby to facilitateassembly and adjustment of related arts, Secured to the block 25 by aradially disposed screw 2%; threaded into said block, is a weight member2i formedof nonmagnetid metal such as brass and preferably shaped on itsexterior surface to the conformat'ion of a cylinder coaxial with thearmature spindle 2i. Disposed on the side of the insulating block 25diametrically opposite the weight member 2! is a further weight member28 generally similar to the member 21, having its exterror surfaceconformed to the same cylindrical contour as" the latter, and supportedfor constrained displacement with respect to the block 25in a manner tobe set forth.

Drilled or otherwise bored, formed to two parallel axes perpendicular tothat of the spindle 2| and radially displaced therefrom on bdth- Sidesto equal distances, are openings passing through the insulating block 25and the two weight members carried thereby; and positioned in saidopenings, and rotatable therein are combined supporting and adjustingscrews 29 and 3d. The screw 29 comprises a slotted head portion lying ina corresponding one of the openings in the weight member 21 and neatlyfitting therein, a radially projecting flange portion 29a interposedbetween said weight member and the mounting block 25, a short portionneatly fitting the corresponding opening in said block, an extendedreduced shank portion 291) also lying within said openingand clearingthe inner wall thereof by asubstantial annular space, a short portion290 provided with a thread, preferably square insection and terminatedby a definite radiallyextending lip portion 29d flush with the inneredge of the cross bav or the 1-- formed by the bleak 25, together withan extended reduced portien 29c projecting into the correspondingopening 3!; in the weight rrlernb'er 28. Said screw 29 is furtherxtended by means of a pin 3-2 of pol= ished metal firrnly fitted in ,abore in said reduced portion 29c, said pin having a clearance fit in awasher 33 fitted firmly in an opening 311 in the weight 28 at the baseof said opening 3|.

The screw 30 may be of the same construction as the screw 29, though, ifdesired, its reduced shank portion (corresponding to portion 29c ofscrew 29) may, as shown, extend completely through the associatedopening 3| in the weight 28, with consequent omission of a pin andwasher corresponding to elements 32 and 33 above described.

The openings 3|, 3| in the weight member 28 are each of considerablylarger diameter than said extensions, and are provided with internalthreads clearing the extended portions of said screws and separatedtherefrom by annular spaces of material width. Fitted upon the innerface of the weight member 28 is a contact piece 35 having connectedthereto an electrical conductor 35; and adapted for electricalengagement therewith is a contact piece 36 fitted to the block andhaving connected thereto an electrical conductor 36, whereby, as saidweight member is displaced toward or from said block, and electricalcircuit may be made or broken between said conductors. One or both facesof said contact pieces is preferably of convex form to permit of slightrocking motion without disturbing electrical engagement.

Surrounding the screw 29 is an extended helical tension spring 3'!formed of Phosphor bronze or similar non-magnetic metal of highelasticity, having several convolutions at one of its extremitiesscrewed into the corresponding threaded opening 3! in the weight member28, and several convolutions near its opposite extremity lying in thegrooves of the thread 290 formed on the screw, a portion of said springextending on to the un-threaded portion 28b of the shank of the screwand terminating in an outwardly extended radial portion adapted to liein a slot 39 milled from the outside surface of the block 25 to theopening therein, whereby to prevent rotation of said spring when thescrew is turned about its axis. The square section of the male thread290 on the screw 29 obviates the tendency which a V-thread would exertto spread the spring and wedge it against the inner walls of the openingin the block 25. The space between the weight member 28 and the innersurface of the block 25, corresponding to the terminal lip 29d of thethread on the screw 29, thus defines the free or effective length of thespring 31; and it will be apparent that as the screw 29 is rotated aboutits axis, since the spring is prevented from rotating with the screw,that portion in engagement with the thread on said screw will functionas a nut, and the effective length of the spring will be varied, therebyproviding an adjustment of the tension which said spring may exert. Asimilar helical spring 38 is extended between the threaded portion ofthe screw 36 and the corresponding threaded opening in the weight member28; and, the springs 3l'38 being adjusted to substantially equaltensions, it will be seen that the contact-pieces 35-36 will bemaintained in engagement witha force which may be varied at will. Theextended flange portions of the screws 29-38, lying between the weightmember 21 and the mounting block 25, being subject to clamping actiontherebetween by the screw 26, serve, when the latter is tightened, tosecure said screws 2930 in their adjusted positions. The pin 32 incooperation with the washer 33 serves to maintain the weight member 28in a proper position with respect to the mounting block 25, thusensuring correct register of the contacts 35--3B, without possibility ofbinding.

Secured to, and supported by, the insulating block 25 is a commutatormember having a number of segments corresponding to that of the poles inthe armature, and adapted for electrical connection to the several coilof the armature winding, the extremity of said commutator remote fromsaid block being reinforced, if desired, as by an insulating band orwasher 4|. The whole armature assembly, including the electromagneticstructure and the weight assembly is balanced to be in neutralequilibrium about the axis of spindle 2| when the weight member 28 is inits constrained position with the contacts 35 and 36 in mutualengagement. The end of the armature shaft 2! remote from the bearing 15is journalled in a bearing 23 centrally positioned in an end plate 44,which, in turn, is carried by four pillars or posts formed preferably asextensions of the mounting bolts i l, and of such extended length as toprovide between the field poles and the bearing 43 clearance toaccommodate the governor weights and the commutator M3. The extremity ofthe shaft 2! projects through the bearing 43, providing for the mountingthereon of a suitable gear or pulley member (not shown in the drawing).

Secured to the end plate 4 5, is an insulating block 45 to Which areclamped by means of a further insulating block 41 and screws 48 a pairof brushes 48 and 58 mutually insulated, and bearing upon the commutator4%] at diametrically opposed positions.

The electrical connections of the motor are shown in Fig. 7. Designatingfor purposes of distinction one set of similar terminals of the severalarmature coils 22 as the inner, and the other set as the outer ends ofsaid coils, the former are directly connected in order to thecorresponding segments of the commutator 40. These connections are madesuch in relation to other elements of the structure that the segmentsengaged at any moment by the brushes are those connected to the windingson the armature poles at that time in transit from the influence of afield pole of one polarity to that of a field pole of opposite polarity,the intermediate segments being connected to those poles which are atthe moment in the positions of most intense field. The outer terminalsof said windings are interconnected in such a manner that those onadjacent poles comprising one half of the armature are connected to one,and those on adjacent poles comprising the other half of the armature tothe other, of the electrical conductors 35 and 36', and thereby to thecontacts 3535. With this connection, it will be seen that forsubstantially every angular position of the armature there will existbetween the brushes 495ii a path including said contacts and two of thearmature coils in series, while with said contacts separated, there willbe an open circuit between said brushes. Upon the two brushes beingconnected to the terminals of a battery 5| or other source ofunidirectional potential a current will flow through one brush to theengaged commutator segment, through the corresponding armature coil, thecontacts 3536, the opposite armature coil, the corresponding commutatorsegment, and the other brush, to the battery, thus tending to magnetizethe armature in a sense perpendicular to the general direction of themain field through the armature, and thereby, according to the wellknownprinciple of the direct-current motor, to produce rotationof thearmature, which rotation will continue indefinitely so long, aspotential from the battery is applied to the brushes, and the angularvelocity of the armature, including the weighted structure, does notexceed a value where centrifugal force exerted upon the weight member 28becomes sufiicient to overcome the influence of the springs 4'0 3l andcause the contacts 35-35 to be separated. Upon the armature acceleratingto a speed where said contacts are opened, the circuit through thewindings will be interrupted, and the armature will tend to reduce itsvelocity, correspondingly decreasing the centrifugal force, until, underthe influence of the springs, the contacts are again closed. Shouldoperating conditions render such desirable, the contacts 235.36 may bebridged by a suitable resistor 52 (shown dotted in Fig. 7) carried .bythe rotating structure and by the selection of whose resistance valuethere may be efiected a wide range of modification of governorperformance.

Because of the straight-line action of the governor, and thefrictionless support of the floating weight 28, the velocity incrementbetween an open and a closed condition of the contacts can be madeextremely small, with the result that governing will take place within avery narrow range of speed variation, giving a correspondingly closeapproach to constant speed operation. Because the floating weight 28 iscarried on a suspension without journals to demand lubrication, the useof oil with its attendant variations in viscosity with temperaturechange is eliminated. The block 25 being formed of an acrylic resin,which is characterized by an expansion temperature coefficient of fromfour to five times that of brass or bronze, has an inherent tendency byits changes in linear dimensions to vary the distance from the axis ofthe shaft 2! to the face of said block upon which rest the flanges ofthe screws 2930, and thereby to vary the tension on the springs 3'l38and ofiset changes in the elasticity of said springs over Wide ranges oftemperature. If desired, the compensation may be increased by formingthe screws 29-30 of Invar or similar material, having a negligible, orzero, temperature coefiicient of linear expansion.

The terms and expressions which I have employed are used as terms ofdescription and not of limitation, and I have no intention, in the useof such terms and expressions, of excluding any equivalents of thefeatures shown and described or portions thereof, but recognize thatvarious modifications are possible within the scope of the inventionclaimed.

I claim:

1. In an electric motor, a stationary field structure, a rotatablearmature structure having an even number of poles, a commutator havingthe same number of mutually insulated segments as the number of saidpoles, coils on said poles to magnetize the same with alternatingpolarity, mutually corresponding ends of coils on one group of adjacentpoles constituting half those on the armature being connected to :afirst common conductor, mutually corresponding ends of coils on thegroup of adjacent poles constituting the other half of the armaturebeing connected to a second common conductor, the free ends of saidcoils being individually connected to said commutator segments, andmeans for interconnecting and for interrupting connection between said.first and second commonconductors.

2. In an electric motor, a stationary field structure, .a rotatablearmature structure having an even number of salient poles, a commutatorhaving the same number of mutually insulated segments as the number ofsaid poles, coils on said poles to magnetize the same with alternatingpolarity, mutually corresponding ends of coils on one group of adjacentpoles constituting half those on the .armature being connected to afirst common conductor, :mutually corresponding ends of coils on thegroup of adjacent poles constituting the other half of the armaturebeing connected to a second common conductor, the free ends of saidcoils being individually connected to said commutator segments, andmeans wholly carried by said armature for interconnecting and forinterrupting connection between said first and second common conductors.

3. In an electric motor, a stationary field structure, a rotatablearmature structure having an even number of salient poles, a commutatorhaving the same number of segments as the number of said poles, Coils onsaid poles to magnetize the same with alternating polarity, mutuallycorresponding ends of coils on one group of adjacent poles constitutinghalf those on the armature being connected to a first common conductor,mutually corresponding ends of coils on the group of adjacent polesconstituting the other half of the armature being connected to a secondcommon conductor, the free ends of said coils being individuallyconnected to said commutator segments, and means wholly carried by saidarmature and comprising a single pair of contacts providinginterconnection between said first and second common conductors.

JOHN L. RUSSELL.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS FOREIGN PATENTS Country Date Great Britain Dec.24, 1935 Number Number

